Brief Description of The Prior Art
A number of types of trenching or ditching machines have previously been devised, and many of them have been commercialized and are currently in use. One type of machine used for forming trenches and ditches is a machine which relies upon an endless, sprocket driven chain which has mounted along its length, a plurality of digging teeth. These teeth operate by a scraping and gouging action to form a trench or ditch as the chain is forced downwardly into the earth, and then moved laterally. The teeth mounted on the chain function to perform both a ditch or trench extension function at the face or leading end of the trench or ditch, and also a trench widening or side wall forming function as a result of the earth removal action of the teeth scraping against the opposed sides of the trench.
One type of tooth used on such endless chains for the purpose of excavating the earth as the chain is continuously driven in rotation by sprockets is the tooth which is illustrated in Nissen U.S. Pat. No. 3,979,843. The Nissen teeth are generally U-shaped in configuration, and are used in an array in which the teeth are faced in alternate directions in their spacing along the chain upon which they are mounted, and are utilized in a trenching operation.
A relatively flat, though slightly concave, generally rectangular digger tooth is shown as it is mounted on an endless chain-type trencher mechanism illustrated in Stewart U.S. Pat. No. 2,714,773. In the Stewart arrangement of teeth on the endless chain, alternate teeth are affixed to opposite sides of the chain, and are faced in opposite directions.
A kerf cutting chain is illustrated in U.S. Pat. No. 2,048,702. The teeth employed on this endless chain are sharply pointed, slightly angled teeth which are arrayed at varying angles with respect to the chain axis in a repeating pattern along the chain.
Trapezoidally-shaped teeth having points oriented to be directed against the face of a continuously projected trench are illustrated in U.S. Pat. No. 3,991,494 as mounted at spaced intervals along the endless chain of an excavating machine.
Another trenching machine is illustrated and described in U.S. Pat. No. 2,817,167. This trenching machine utilizes U-shaped teeth secured at spaced intervals along an endless chain. The teeth are cupped inwardly and then outwardly in alternating sequence. In the words of the patentee, the digger teeth project outwardly and laterally from certain links of the endless chain, and are formed to dig into the ground and carry the earth upwardly out of the ditch.
Cup-shaped teeth having a wide leading edge and a diminished trailing edge at the end of a trapezoidally-shaped principal plate are shown in Horton U.S. Pat. No. 3,846,922. Here the teeth are mounted upon a continuous or endless ditcher chain, and each tooth in the array of teeth along the chain appears to be substantially identically oriented with respect to the axis of the chain.
Cup-shaped or C-shaped teeth which are alternately faced inwardly and outwardly along the length of an endless chain employed in a trenching apparatus are illustrated and described in Albertson U.S. Pat. No. 4,475,604. This patent describes a mobile trenching machine, and the cup-shaped teeth here illustrated as mounted upon the endless chain of the trenching machine are of a widely used, commercially available-type.
A somewhat similar cup-shaped tooth which includes a shank portion for mounting to an endless chain, and a cup-shaped upper cutting portion extending out from the shank portion, and carrying a cutting edge, is shown in Schmidt U.S. Pat. No. 2,519,075. In the Schmidt patent, the teeth are, in each case, faced toward the central axis of the chain. Stated differently, the convex outer side of each tooth faces toward the trench wall and away from the axis of the chain.
One of the advantages which is said to characterize the cup-shaped teeth or blades used on the endless chain of the Schmidt patent is that these teeth completely eliminate the need for buckets or spades in order to elevate to the surface, the particles of earth which have been cut away from the walls and face of the trench. The cutter blades, or teeth, are placed on the endless chain in alternately right and left hand array--that is, a right hand cutter blade is affixed to the chain, followed by a left hand cutter blade, with the right and left hand cutter blades or teeth being secured to opposite sides of the chain and thus opening inwardly in each case. The shank plate which is provided serves as an integral part of the chain. Each of the cutter teeth has a sharply tapered or sharpened leading edge and a trailing edge. Conventional roller chain pins extend through the apertures formed in the mounting shank portions on the cutter blades or teeth.
Generally L-shaped cutter teeth are mounted on an endless chain used in a mining machine described and illustrated in Teller U.S. Pat. No. 979,597. The pointed short leg of the "L" is oriented forward approximately parallel to the chain axis. The shank portions of the teeth used in the Teller mining machine are mounted on a central axis of the endless chain, and are arrayed in sets of three teeth. The angulation of each tooth of the three varies slightly with respect to the axial plane of the chain. Tooth function is generally of the "point attack" or "pick" cutter type.
Another type of generally angled or V-shaped cutter tooth developed for utilization in mining machines is that which is illustrated in U.S. Pat. No. 2,645,471 to King. This tooth also has the pointed short leg of the "V" oriented forward approximately parallel to the chain axis, and tooth function is generally of the "point attack" or "pick" cutter type. The leading face or edge of the cutter tooth of King carries a bead of overlay metal which is a self-hardening material made up of a selected balance of alloy metals. The fused overlay of abrasion resistant alloy extends along a certain critical area on the cutter bit or tooth to aid in preventing wear and reduction of the working height of the tooth in a short period of time.